Abstract

2669

Malignant melanoma have a bad prognosis (median survival: 6-7 months, 5-year survival ca 6%) mainly due to rapid development of liver, brain and lung metastases. Because of its rising incidence in Caucasian population, this malignancy has become an important health issue. The aim of this study was to investigate the anti-melanoma potency of ilimaquinone, a sesquiterpene quinone isolated from Smenospongia species collected in Red sea. METHODS The resazurin reduction test (a cytotoxicity assay) and FACS analysis were used to assess the antiproliferative and pro-apoptotic effect of the quinone on human primary fibroblasts and human M4Beu cells (a pigmented metastasis-derived malignant melanoma line). Ceramide was determined by HPTLC in the presence or absence of pharmacological inhibitors . RESULTS Ilimaquinone exhibited more pronounced antiproliferative effects on M4Beu cells than on primary fibroblasts suggesting a therapeutic margin. Inhibition of M4Beu survival was dose-dependant and attributable to cell-cycle blockade in G1 and, at higher concentration induction of apoptosis. Apoptosis was correlated with ceramide triggering. The release of ceramide was reduced by co-treatment with myriocin (an inhibitor of serine-palmitoyl transferase) or N acetyl cysteine (Nac, an inhibitor of neutral sphingomyelinase). Note that if Nac pre-treatment strongly impaired apoptosis, myriocin pre-treatment has only little inhibitory effect. CONCLUSION These data indicate that ilimaquinone has a selectivity for melanoma cells and inhibits the proliferation of this metastatic malignant melanoma line through cell-cycle disturbance and induction of apoptosis. They show that ilimaquinone treatment triggers ceramide signalling in human M4Beu cells and, that the pool of ceramide is partly due to “de novo” ceramide synthesis and, partly to sphingomyelin hydrolysis by neutral sphingomyelinase. The strong reduction of ceramide release after Nac pre-treatment indicates that neutral sphingomyelinase activity is required for induction of apoptosis. Altogether, our data suggest a possible value of sesquiterpene quinone derivatives from Smenospongia sp for treatment of metastatic melanoma. Additional investigations are needed to verify this hypothesis.